Let's say you have a flash head banner on the page that you are trying to optimize. Let's also assume that you've incorporated an underlying HTML banner for SEO purposes. Now, do you think Google actually "reads" flash content and can penalize you for not using the same content on both headers?
Despite "Google can read" flash content, it reads everything from flash as plain text, I mean, you can't count with semantic features and the weight they brings as HTML do, like H1, H2, strong....
So, if you are really serious about optimizing give up on flash. If you really can't drop flash, use same text, with correct markup on proper elements. Also make sure you put the header content as an alternative making use of a noscript tag.